Date of Award
Doctor of Philosophy
Dr. Craig E. Tweedie
Arctic vegetation communities are responding to climate warming through shifts in species composition and diversity but most observations have been made over relatively short time frames, and/or in association with experimental manipulations. Because vegetation plays a key role in regulating ecosystem productivity, nutrient cycling, surface energy budgets, and trophic interactions in the Arctic, there is a need to better understand shifts in tundra vegetation communities over decadal time scales. Understanding these shifts and their impact on ecosystem structure and function in the Arctic has important implications for predicting the future state of both the Arctic and the Earth System. Long term monitoring, and/or rediscovering, rescuing, securing, and resampling historic research sites to ascertain past and future trajectories of decadal time scale change are among the few approaches for advancing knowledge of how Arctic terrestrial ecosystem properties and processes are likely to change decadal time scales.
The primary objective of this International Polar Year (IPY) dissertation project was to determine how key structural characteristics of high-latitude arctic terrestrial ecosystems have changed over the past three to five decades at three different historic research locations spanning the high and low Arctic. Historic sites were established by Dr Patrick J. Webber early in his career using the same methodology and include (1) the International Biological Program (IBP) research sites established in 1972 near Barrow, Alaska, (2) the Research on Arctic Tundra Environments (RATE) research sites established in 1975 near Atqasuk, Alaska, and (3) his dissertation research sites established in 1964 in North-Central Baffin Island, Nunavut, Canada. Historic IBP sites established in alpine tundra on Niwot Ridge, Colorado were also used in a synthesis that compared change across all locations and tundra vegetation types. All sites measured 1 m x 10 m and consisted of ten contiguous 1 m2 plots that were resampled during summer field seasons when sites were snow free between 2008 and 2010. Percent cover for vascular, non-vascular, and lichen species were estimated at all three sites.
The following key questions were addressed by resampling these historic sites:
I. Is there evidence of vegetation community change?
II. Which vegetation communities are changing most/least and is there evidence of a shift in the rate of change over time?
III. Are changes in specific vegetation functional groups driving community change?
IV. Are diversity, richness and individual species changing?
V. Along which environmental gradients are changes occurring and what are the likely biophysical factors driving change?
VI. Have patterns of primary succession following deglaciation changed over time at Baffin Island, Canada?
VII. Do herbivores mask or facilitate decade time-scale vegetation community change at Barrow, Alaska?
VIII. How have vegetation communities, species richness, evenness, and diversity changed across the tundra, and how does this change differ between long-term and short-term sampling intervals?
Vegetation community change varied by location and vegetation community type, and within a particular site. At Baffin Island, Canada species richness did not change but diversity increased over a 45-year period. All vegetation communities shifted in a similar direction, and indicated landscape drying. Young successional sites show that changepoints for vegetation cover, species richness, and Shannon Index of diversity are earlier for 2009 sites less than 200 years of age, suggesting that rates of succession are accelerating. In Barrow, Alaska species richness and diversity increased over the 38 year sampling period, wet vegetation communities changed more than dry communities, and the response of vegetation to lemming population cycles were found to mask long-term changes in vegetation change. In Atqasuk, Alaska species richness and diversity did not change, but evenness increased significantly. Vegetation communities changed little over the 34-year sampling period, however, the change documented for many communities indicated a shift towards a wetter state. Vegetation community change was also found to be accelerating over the last decade for sites near Atqasuk, and that the rate of change in diversity is accelerating.
These findings demonstrate that the response of arctic vegetation communities to global change, which includes climate change, is spatiotemporally complex. Considering the importance of vegetation community assemblage and ecosystem structure to ecosystem function and the potential for arctic terrestrial ecosystem change to impact other components of the Arctic and Earth System, it is important to continue to monitor change in tundra landscapes over decadal time scales. The Back to the Future approach has demonstrated new capacities for achieving such knowledge and has the potential to be scaled across the Arctic and other disciplines to advance systems understanding and response to global change.
Received from ProQuest
Villarreal, Sandra, "International Polar Year (IPY) Back To The Future (BTF): Changes In Arctic Ecosystem Structure Over Decadal Times Scales" (2013). Open Access Theses & Dissertations. 1956.